[Rapid diagnosis of tuberculosis].
Two systems, the newly developed Mycobacteria Growth Indicator Tube (MGIT) and biphasic Septi-Chek AFB based on liquid media, proved to be significantly better than the egg-based solid media for the isolation of mycobacteria from clinical specimens. The difference in the rates of isolation of bacteria between the two groups of media was more remarkable with smear-negative specimens. The isolation of the Mycobacterium tuberculosis complex by MGIT occurred 8 days previous to the isolation by the conventional Ogawa method. The mean time for detecting M. tuberculosis complex by Septi-Chek AFB was similar to those of the Ogawa method. A greater difference in isolation time was observed for mycobacteria other than M. tuberculosis (MOTT) isolates. These results indicate that the MGIT and Septi-Chek AFB systems based on liquid media are efficient for the recovery of mycobacteria. PCR and other nucleic acid amplification methods are widely used for the detection of M. tuberculosis in clinical specimens. Although the sensitivities of the Gen-Probe Amplified Mycobacteria Direct Test (MTD) and Amplicor Mycobacteria for the detection of the M. tuberculosis complex appear to be similar to the sensitivity of the culture method using the Septi-Chek AFB, the two methods should be quite useful for rapid detection of M. tuberculosis infections. On the other hand, two cooperative blind studies conducted between 6 to 9 laboratories to estimate the reliability and reproducibility of these two commercially available kits revealed the necessity of good laboratory practice and development of reference reagents to monitor the performance of the whole assay, including pretreatment of clinical specimens. Considerable progress has been made in recent years toward understanding the molecular basis of the resistance to antituberculosis drugs, isoniazid (katG, inhA, ahpC), rifampin (rpoB), pyrazinamide (pncA), streptomycin (rpsL, rrs), ethambutol (embB), and fluoroquinolones (gyrA). Most cases of resistance are related usually to simple nucleotide substitutions rather than to acquisition of new genetic elements. Multidrug-resistant isolates of M. tuberculosis arise as a consequence of sequential accumulation of mutations conferring resistance to single therapeutic agents. The basis of resistance is not able to be explained yet in a substantial percentage of strains (> 90%) for other antituberculosis drugs than rifampin. Further studies are required to fully understand the molecular mechanisms of resistance.
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Research Institute of Tuberculosis, Japan Anti-Tuberculosis Association, Tokyo, Japan.
D004269:DNA, Bacterial / Q000032:analysis; D005798:Genes, Bacterial; D019450:Genes, MDR; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D009169:Mycobacterium tuberculosis / Q000235:genetics / Q000302:isolation & purification*; D016133:Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D014376:Tuberculosis / Q000175:diagnosis* / Q000382:microbiology; D018088:Tuberculosis, Multidrug-Resistant
D004269:DNA, Bacterial